Movie scenes that made you crap your pants.

[Fireball]

My two youngest sons were traumatized by the "Titanic" movie when they were young. I indeed did not enjoy seeing the frozen dead floating in the water, but that wasn't a crap-my-pants-worthy scene.

A truly scary scene for me was at a matinee at the "local" theater, presenting, "Head of the Gorgon". When her head was cut off, I had a fear that I would be stiff as well...and not in a way I would enjoy.

Perhaps a bit off topic:

Do you think that violence in films/TV/Video games desensitises children specifically, and people generally?

I think they do. The only evidence  I  can give is the fact that over a long period I began to watch and enjoy forensic crime shows, including the ones with graphic imagery of bodies having an autopsy. EG NCIS

Yes. Repeated viewing of violence desensitizes people, imo. I view those sorts of shows with disgust over the dehumanization of the deceased. I DO NOT enjoy forensic programming. I went into physics instead of medicine. My main revulsion was to the sight of blood. I did consider a career in medicine, but my aversion to blood (plus, my family being poor as piss on a plate) pretty much precluded that.